Separation process for the product streams resulting from the dehydrogenation of hydrocarbons

ABSTRACT

A process for the separation and recovery of the product stream resulting from the dehydrogenation of dehydrogentable hydrocarbons which process utilizes an integrated system for the recovery of liquid olefin product by use of a compression system, a pressure swing adsorption unit and a chiller system to concentrate the olefin poroduct.

FIELD OF THE INVENTION

The present invention is directed towards an improved process for theseparation and recovery of the product stream resulting fromdehydrogenation of dehydrogenatable hydrocarbons. More specifically, theinvention utilizes an integrated system for the recovery of olefinproduct liquid by the use of a compression system, a pressure swingadsorption unit and a chiller system to concentrate the olefin productliquid by rejecting hydrogen and light gaseous hydrocarbons which werenot completely rejected in the pressure swing adsorption unit.

BACKGROUND OF THE INVENTION

Dehydrogenating hydrocarbons is an important commercial hydrocarbonconversion process because of the great demand for dehydrogenatedhydrocarbons for the manufacture of various chemical products such asdetergents, high octane motor fuels, pharmaceutical products, plastics,synthetic rubbers, polymerization monomers and other products well knownto those skilled in the art. Processes for the dehydrogenation of lightacyclic hydrocarbons are well known to those skilled in the hydrocarbonconversion arts. For instance, the dehydrogenation of C₂ -C₅ paraffinsis well known. Because the light paraffins are relatively volatile, amore complicated separation scheme and a bulk condensation is normallyrequired to effect the separation of the product olefins from the lightby-products and hydrogen which are simultaneously produced in theprocess. It is therefore believed that U.S. Pat. No. 4,381,418(Gewartowski et al) is pertinent for its teaching of a catalyticdehydrogenation process for C₂ ⁺ normally gaseous paraffinichydrocarbons and the recovery of products of the reaction. U.S. Pat.Nos. 4,430,517 and 4,486,547 issued to Imai et al and U.S. Pat. No.4,469,811 issued to Lucien are believed pertinent for their teaching ofcatalysts and operating conditions which can be employed for thedehydrogenation of low molecular weight parrafins.

Pressure swing adsorption (PSA) provides an efficient and economicalmeans for separating a multi-component gas stream containing at leasttwo gases having different adsorption characteristics. The more-stronglyadsorbable gas can be an impurity which is removed from theless-strongly adsorbable gas which is taken off as product; or, themore-strongly adsorbable gas can be the desired product, which isseparated from the less-strongly adsorbable gas. For example, it may bedesirable to remove carbon monoxide and light hydrocarbons from ahydrogen-containing feed stream to produce a purified (99⁺ %) hydrogenstream for a hydrocracking or other catalytic process where theseimpurities could adversely affect the catalyst or the reaction. On theother hand, it may be desirable to recover more-strongly adsorbablegases, such as ethylene, from a feed to produce an ethylene-enrichedproduct.

In pressure swing adsorption, a multi-component gas is typically fed toat least one of a plurality of adsorption beds at an elevated pressureeffective to adsorb at least one component, while at least one othercomponent substantially passes through. At a defined time, feed to theadsorber is terminated and the bed is depressurized by one or moreco-current to the direction of feed depressurization steps whereinpressure is reduced to a level which permits the separated,less-strongly adsorbed component or components remaining in the bed tobe drawn off without significant removal of the more strongly adsorbedcomponents. Then, the bed is depressurized by a countercurrentdepressurization step wherein the pressure on the bed is further reducedby withdrawing desorbed gas countercurrently to the direction of feed.Finally, the bed is purged and repressurized.

Those skilled in the art of hydrocarbon processing, more particularlythe dehydrogenation of hydrocarbons, are constantly searching for waysto recover a liquid product from a dehydrogenation zone in the mostconvenient and economical manner.

BRIEF SUMMARY OF THE INVENTION

The invention provides a process for the production of olefinichydrocarbons at essentially 100% recovery as well as an enrichedhydrogen product without requiring severe cryogenic processingconditions. This integrated process achieves the demonstrated advantagesby the use of a compression system for the initial recovery of aparaffin/olefin liquid product stream from a vapor-liquid separator andthe vapor comprising hydrocargon and hydrogen is removed from thevapor-liquid separator and introduced into a pressure swing adsorption(PSA) unit. The PSA unit produces a hydrogen-rich gaseous stream whichmay be used for recycle and a tail gas containing the previouslyadsorbed hydrocarbon vapor which is chilled to produce a liquidhydrocarbon stream.

A vapor stream is recovered from the chiller and contains hydrogen andsmall quantities of hydrocarbon which stream is recycled to thedehydrogenation zone effluent and the hydrocarbon is subsequentlyrecovered. In this manner, a product recovery of up to 100% is achievedand hydrogen is rejected from the system except for the hydrogen removedas dissolved hydrogen in the liquid hydrocarbon product.

One broad embodiment of the present invention may be characterized as aprocess for the dehydrogenation of a dehydrogenatable hydrocarbon whichprocess comprises: (a) contacting the dehydrogenatable hydrocarbon witha dehydrogenation catalyst in a dehydrogenation zone at dehydrogenationconditions to produce a hydrocarbon effluent stream comprisingdehydrogenated hydrocarbons, unconverted dehydrogenatable hydrocarbonsand hydrogen; (b) compressing the hydrocarbon effluent stream comprisingdehydrogenated hydrocarbons, unconverted dehydrogenatable hydrocarbonsand hydrogen to produce a compressed stream; (c) cooling the compressedstream to a temperature less than about 150° F. (65° C.); (d)introducing the resulting compressed, cooled stream produced in step (c)into a vapor-liquid separator; (e) withdrawing from the vapor-liquidseparator a liquid stream comprising at least a portion of thedehydrogenated hydrocarbons and the unconverted dehydrogenatablehydrocarbon contained in the hydrocarbon effluent stream; (f)withdrawing from the vapor-liquid separator a hydrogen-rich gaseousstream comprising at least a portion of the dehydrogenated hydrocarbonsand unconverted dehydrogenatable hydrocarbons; (g) passing thehydrogen-rich gaseous stream from step (f) to a first adsorber bedcontaining adsorbent having adsorptive capacity for hydrocarbons ateffective adsorption conditions; (h) withdrawing a hydrogen-rich gaseousstream having a reduced concentration of hydrocarbons from the firstadsorber bed; (i) withdrawing a stream rich in hydrocarbons from asecond adsorber bed containing adsorbent having adsorptive capacity forhydrocarbons which bed has become loaded with hydrocarbons and isundergoing desorption; (j) cooling the stream rich in hydrocarbons fromstep (i) to a temperature less than about 100° F. (38° C.); (k)introducing the resulting cooled stream produced in step (j) into avapor-liquid separator to produce a vapor stream comprising hydrogen anda liquid stream comprising dehydrogenated hydrocarbon; (l) recycling thevapor stream comprising hydrogen recovered in step (k) to step (b); and(m) recovering a hydrocarbon stream comprising a dehydrogenatedhydrocarbon.

Another broad embodiment of the present invention may be characterizedas a process for the dehydrogenation of a dehydrogenatable hydrocarbonwhich process comprises: (a) contacting the dehydrogenatable hydrocarbonwith a dehydrogenation catalyst in a dehydrogenation zone atdehydrogenation conditions which include a temperature from about 752°F. (400° C.) to about 1652° F. (900° C.), a pressure from about 0.01 toabout 10 atmospheres absolute, a liquid hourly space velocity from about0.1 to about 100 hr⁻¹ and a hydrogen to hydrocarbon mole ratio fromabout 0.01:1 to about 40:1 to produce a hydrocarbon effluent streamcomprising dehydrogenated hydrocarbons, unconverted dehydrogenatablehydrocarbons and hydrogen; (b) compressing the hydrocarbon effluentstream comprising dehydrogenated hydrocarbons, unconverteddehydrogenatable hydrocarbons and hydrogen to a pressure in the rangefrom about 1 psig (6.895 kPa gauge) to about 1000 psig (6895 kPa gaugeto produce a compressed stream; (c) cooling the compressed stream to atemperature in the range from about 60° F. (16° C.) to about 120° F.(49° C.); (d) introducing the resulting compressed, cooled streamproduced in step (c) into a vapor-liquid separator; (e) withdrawing fromthe vapor-liquid separator a liquid stream comprising at least a portionof the dehydrogenated hydrocarbons and the unconverted dehydrogenatablehydrocarbon contained in the hydrocarbon effluent stream; (f)withdrawing from the vapor-liquid separator a hydrogen-rich gaseousstream comprising at least a portion of the dehydrogenated hydrocarbonsand unconverted dehydrogenatable hydrocarbons; (g) passing thehydrogen-rich gaseous stream from step (f) to a first adsorber bedcontaining adsorbent having adsorptive capacity for hydrocarbons ateffective adsorption conditions; (h) withdrawing a hydrogen-rich gaseousstream having a reduced concentration of hydrocarbons from the firstadsorber bed; (i) withdrawing a stream rich in hydrocarbons from asecond adsorber bed containing adsorbent having adsorptive capacity forhydrocarbons which bed has become loaded with hydrocarbons and isundergoing desorption; (j) cooling the stream rich in hydrocarbons fromstep (i) to a temperature in the range from about -20° F. (-29° C.) toabout 100° F. (38° C.); (k) introducing the resulting cooled streamproduced in step (j) into a vapor-liquid separator to produce a vaporstream comprising hydrogen and a liquid stream comprising dehydrogenatedhydrocarbon; (l) recycling the vapor stream comprising hydrogenrecovered in step (k) to step (b); and (m) recovering a hydrocarbonstream comprising a dehydrogenated hydrocarbon.

Other embodiments of the subject invention encompass further detailssuch as preferred feedstocks, dehydrogenation catalysts, adsorbents andoperating conditions, all of which are hereinafter disclosed in thefollowing discussion of each of these facets of the invention.

BRIEF DESCRIPTION OF THE DRAWING

The drawing is a simplified process flow diagram of a preferredembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Olefinic hydrocarbons are one of the major building blocks of a largenumber of petrochemical products. Olefinic hydrocarbons are also usefulin petroleum refineries for the production of motor fuel blendingcomponents. The process of the present invention possesses utility inproviding facile production of these olefinic hydrocarbons. Based uponthe commercial desirability to produce olefinic hydrocarbons, there is aconstant search for techniques to lower the cost of production of theseolefins. We have discovered an integrated dehydrogenation productsseparation process with enhanced economics and the details of whichprocesses are herein described.

The term "dehydrogenatable hydrocarbons" as utilized herein is meant torefer to all classes of hydrocarbons containing saturated carbon bondswhich have the potential for forming one or more unsaturated bondsthrough the process of dehydrogenation. The preferred dehydrogenatablehydrocarbons of the present invention consist of paraffinic typehydrocarbons. More specifically, the paraffin hydrocarbon charge stockof the present invention may contain from 2 carbon atoms to about 30carbon atoms. Representative members of this class are: ethane, propane,butane, pentane, hexane, heptane, nonane, decane, undecane, dodecane,tridecane, tetradecane, pentadecane, hexadecane, heptadecane,octadecane, and mixtures thereof. A particularly important class ofcharge stocks include ethane, propane, butane, pentane and mixturesthereof and which are readily prepared by the fractionation ofrelatively low boiling point hydrocarbon fractions. Another importantcharge stock contains normal paraffins of about 10 to about 15 carbonatoms since these produce a mono-olefin which can be utilized to makedetergents having superior biodegradability and detergency. For example,a mixture containing a 4 or 5 homolog spread, such as C₁₁ to C₁₄, C₁₀ toC₁₃, C₁₁ to C₁₅, provides an excellent charge stock. Moreover, it ispreferred that the amount of nonnormal hydrocarbons present in thisnormal paraffin stream be kept at low levels. Thus, it is preferred thatthis stream contain greater than 90 wt. % normal paraffin hydrocarbons,with best results achieved at purities in the range of 96-99 wt. % ormore. Although various types of hydrocarbon feedstocks may be utilizedin the process of the present invention, for purposes of specificexemplification, a feed stream comprising propane is described indetail.

The selected dehydrogenatable hydrocarbon feedstock is introduced into adehydrogenation zone containing dehydrogenation catalyst and operated atdehydrogenation conditions to convert at least a portion of thedehydrogenatable hydrocarbons to produce a hydrocarbon stream comprisingdehydrogenated hydrocarbons and unconverted dehydrogenatablehydrocarbons. Preferably, the unconverted dehydrogenatable hydrocarbonsare separated and recycled to the dehydrogenation zone together with thefresh feedstock.

The dehydrogenation catalyst may be employed in a fixed bed, fluidizedbed, or a moving bed. Moreover, the dehydrogenation catalytic reactionzone may consist of multiple catalyst beds. In one such system, thecatalyst is employed within an annular bed through which it is movablevia gravity flow. In such a system, it is common practice to removecatalyst from the bottom of the reaction zone, regenerate it and thenreturn it to the top of the reaction zone. Any suitable dehydrogenationcatalyst may be used in the process of the present invention. Generally,the preferred catalyst comprises a platinum group metal component, analkali metal component and a porous inorganic carrier material. Thecatalyst may also contain promoter metals which advantageously improvethe performance of the catalyst. It is preferable that the porouscarrier material of the dehydrogenation catalyst be an absorptive highsurface area support having a surface area of about 25 to about 500 m²/g. The porous carrier material should be relatively refractory to theconditions utilized in the reaction zone and may be chosen from thosecarrier materials which have traditionally been utilized in dualfunction hydrocarbon conversion catalysts. A porous carrier material maytherefore be chosen from an activated carbon, coke or charcoal, silicaor silica gel, clays and silicates including those syntheticallyprepared and naturally occurring, which may or may not be acid-treatedas, for example, attapulgus clay, diatomaceous earth, kieselguhr,bauxite; refractory inorganic oxide such as alumina, titanium dioxide,zirconium dioxides magnesia, silica alumina, alumina boria; crystallinealumina silicates such as naturally occurring or synthetically preparedmordenite or a combination of one or more of these materials. Thepreferred porous carrier material is a refractory inorganic oxide, withthe best results being obtained with an alumina carrier material. Thealuminas, such as gamma alumina, give the best results in general. Thepreferred catalyst will have a gamma alumina carrier which is in theform of spherical particles having relatively small diameters on theorder of about 1/16".

The preferred dehydrogenation catalyst also contains a platinum groupmetal component. Of the platinum group metals, which include palladium,rhodium, ruthenium, osmium or iridium, the use of platinum is preferred.The platinum group component may exist within the final catalystcomposite as a compound such as an oxide, sulfide, halide, oxysulfide,etc., of an elemental metal or in combination with one or more otheringredients of the catalyst. It is believed that the best results areobtained when substantially all the platinum group components exist inthe elemental state. The platinum group component generally comprisesfrom about 0.01 to about 2 wt. % of the final catalytic composite,calculated on an elemental basis. It is preferred that the platinumcontent of the catalyst be between about 0.2 and 1 wt. %. The preferredplatinum group component is platinum, with palladium being the nextpreferred metal. The platinum group component may be incorporated intothe catalyst composite in any suitable manner such as by coprecipitationor cogelation with the preferred carrier material, or by ion-exchange orimpregnation of the carrier material. The preferred method of preparingthe catalyst normally involves the utilization of a water-solubledecomposable compound of a platinum group metal to impregnate thecalcined carrier material. For example, the platinum group component maybe added to the support by commingling the support with an aqueoussolution of chloroplatinum or chloropalladic acid. An acid such ashydrogen chloride is generally added to the impregnation solution to aidin the distribution of the platinum group component throughout thecarrier material.

Additionally, the preferred catalyst contains an alkali metal componentchosen from cesium, rubidium, potassium, sodium, and lithium. Thepreferred alkali metal is normally either potassium or lithium,depending on the feed hydrocarbon. The concentration of the alkali metalmay range from about 0.1 to 3.5 wt. %, but is preferably between 0.2 andabout 2.5 wt. % calculated on an elemental basis. This component may beadded to the catalyst by the methods described above as a separate stepor simultaneously with the solution of another component.

As noted previously, the dehydrogenation catalyst may also containpromoter metal. One such preferred promoter metal is tin. The tincomponent should constitute about 0.01 to about 1 wt. % tin. It ispreferred that the atomic ratio of tin to platinum be between 1:1 andabout 6:1. The tin component may be incorporated into the catalyticcomposite in any suitable manner known to effectively disperse thiscomponent in a very uniform manner throughout the carrier material.Thus, the component may be added to the carrier by coprecipitation.

A preferred method of incorporating the tin component involvescoprecipitation during the preparation of the preferred carriermaterial. This method typically involves the addition of a suitablesoluble tin compound, such as stannous or stannic chloride to an aluminahydrosol, mixing these ingredients to obtain a uniform distributionthroughout the sol and then combining the hydrosol with a suitablegelling agent and dropping the resultant admixture into an oil bath. Thetin component may also be added through the utilization of a solubledecomposable compound of tin to impregnate the calcined porous carriermaterial. A more detailed description of the preparation of the carriermaterial and the addition of the platinum component and the tincomponent to the carrier material may be obtained by reference to U.S.Pat. No. 3,745,112.

The dehydrogenation conditions which will be employed in the process ofthe present invention will of course vary depending on such factors ascatalyst activity, feedstock, and desired conversion. A general range ofconditions which may be employed for dehydrogenation of a lighthydrocarbon include a temperature of from about 752° F. (400° C.) toabout 1652° F. (900° C.) a pressure of from about 0.01 to about 10atmospheres absolute, a liquid hourly space velocity between about 0.1and about 100 hr.⁻¹ and a hydrogen mole ratio from about 0.01:1 to about40:1.

In accordance with the present invention, a hydrocarbon stream, forexample, comprising propylene, propane, ethylene, ethane, methane,hydrogen and, in some cases, carbon dioxide, carbon monoxide and wateris removed from the dehydrogenation reaction zone and is compressed to apressure in the range from about 1 psig (6.895 kPa gauge) to about 1000psig (6895 kPa gauge). The resulting compressed hydrocarbon stream iscooled to a temperature in the range from about 60° F. (16° C.) to about150° F. (65° C.) and introduced into a vapor-liquid separator. A liquidstream comprising at least a portion of the dehydrogenated hydrocarbonsand the unconverted dehydrogenatable hydrocarbons contained in theeffluent from the dehydrogenation zone is withdrawn from thevapor-liquid separator and recovered. A hydrogen-rich gaseous streamcomprising at least a portion of the dehydrogenated hydrocarbons andunconverted dehydrogenatable hydrocarbons is removed from thevapor-liquid separator and is passed to an adsorber bed containingadsorbent having adsorptive capacity for hydrocarbons at effectiveadsorption conditions. An effluent from the adsorber bed comprising ahydrogen-rich gaseous stream and having a reduced concentration ofhydrocarbons is recovered. At least a portion of the hydrogen-richgaseous stream may be recycled to the dehydrogenation reaction zone,used to regenerate a spent adsorber bed, or used in some other usefulmanner. Preferably the adsorber bed is a part of an integrated pressureswing adsorption (PSA) process whereby a continuous adsorber operationcan be obtained while simultaneously regenerating a spent adsorber bed.

The present invention can be performed using virtually any adsorbentmaterial in the adsorber beds that has a preferential capacity forhydrocarbons as compared to hydrogen. Suitable adsorbents known in theart and commercially available include crystalline molecular sieves,activated carbons, activated clays, silica gels, activated aluminas andthe like.

It is often desirable when using crystalline molecular sieves that themolecular sieve be agglomerated with a binder in order to ensure thatthe adsorbent will have suitable physical properties. Although there area variety of synthetic and naturally-occurring binder materialsavailable such as metal oxides, clays, silicas, aluminas,silica-aluminas, silica-zirconias, silica-thorias, silica-berylias,silica-titanias, silica-alumina-thorias, silica-alumina-zirconias,mixtures thereof and the like. Clay-type binders are preferred andexamples which may be employed to agglomerate the molecular sievewithout substantially altering the adsorptive properties of the zeoliteare attapulgite, kaolin, volclay, sepiolite, polygorskite, kaolinite,bentonite, montmorillonite, illite and chlorite. The choice of asuitable binder and methods employed to agglomerate the molecular sievesare generally known to those skilled in the art and need not be furtherdescribed herein.

The PSA cycle used in the present invention preferably includes thesteps of adsorption, at least one co-current depressurization step,countercurrent desorption, purge and repressurization. Thus cycle stepsare typically described with reference to their direction relative tothe adsorption step. The cycle steps wherein the gas flow is in aconcurrent direction to the adsorption step are known as "co-current"steps. Similarly, cycle steps wherein the gas flow is countercurrent tothe adsorption step are known as "countercurrent" steps. During theadsorption step the feed stream is passed to the adsorber bed at anelevated adsorption pressure in order to cause the adsorption of thehydrocarbons and produce a hydrogen-rich gaseous stream. During theco-current depressurization steps the pressure in the depressurizing bedis released and the effluent obtained therefrom, which is rich inhydrogen, is passed in a countercurrent direction to another adsorberbed undergoing purge or repressurization. Typically, more than oneco-current depressurization step is used wherein a first equalizationstep is performed after which a provide purge step is initiated whereinthe adsorber bed is further co-currently depressured to provide a purgegas that is relatively impure with respect to the adsorbed component andthus is suitable for use as a purge gas. Optionally, a portion ofhydrogen-rich adsorption effluent gas having a reduced concentration ofhydrocarbons or an externally supplied gas can be used to supply thepurge gas. Upon the completion of the co-current depressurization step,if employed, the adsorber bed is countercurrently depressurized to adesorption pressure in order to desorb the hydrocarbons. Upon completionof the desorption step, the adsorber bed is purged countercurrently withpurge gas typically obtained from another bed. Finally, the adsorber bedis repressurized, first, typically with equalization gas from otheradsorber beds and then with feed or product gas to adsorption pressure.Other additional steps known to those skilled in the art, such as aco-purge step wherein the adsorber bed is co-currently purged of theless strongly adsorbed components at an elevated pressure such as theadsorption pressure with a purge stream comprising hydrocarbons, can beemployed.

The adsorber bed may suitably be operated at a pressure in the rangefrom about 1 psig (6.895 kPa gauge) to about 1000 psig (6895 kPa gauge).The operating temperature for the adsorber bed may be selected from therange from about -20° F. (-29° C.) to about 150° F. (65.5° C.). Theseoperating condition ranges are suitable for both adsorption anddesorption. Additional operating conditions of the adsorber bed such ascycle times and rates of depressurization, for example, are not criticalto the present invention and may readily be selected by a person skilledin the art.

In accordance with the present invention, the desorption streamcontaining hydrocarbons and hydrogen is removed from the PSA section andcooled to a temperature in the range from about -20° F. (-29° C.) toabout 100° F. (38° C.) and a vapor-liquid separation is performed. Aliquid stream containing dehydrogenated hydrocarbons and unconverteddehydrogenatable hydrocarbons is withdrawn and recovered. Ahydrogen-rich gaseous stream containing a minority of the dehydrogenatedhydrocarbons and unconverted dehydrogenatable hydrocarbons is removedand subsequently passed as a recycle stream to the adsorption zone.

In accordance with the present invention, one product is a hydrocarbonliquid stream containing dehydrogenated hydrocarbon, unconvertedhydrocarbon and dissolved hydrogen with essentially complete recovery ofall hydrocarbon. This complete recovery of the hydrocarbon compounds iseconomically attractive and this hydrocarbon liquid stream may then beseparated by means of conventional techniques to produce an olefinstream and an unconverted hydrocarbon stream which may then be recycledto the dehydrogenation zone. Another product is a high-purity hydrogenstream having a low level of hydrocarbon with essentially all of thehydrogen recovered except for that dissolved in the hydrocarbon liquidstream.

DETAILED DESCRIPTION OF THE DRAWING

In the drawing, the process of the present invention is illustrated bymeans of a simplified flow diagram in which such details as pumps,instrumentation, heat-exchange and heat-recovery circuits, compressorsand similar hardware have been deleted as being non-essential to anunderstanding of the techniques involved. The use of such miscellaneousequipment is well within the purview of one skilled in the art.

With reference now to the drawing, a dehydrogenatable hydrocarbon feedstream comprising propane and trace quantities of butane is introducedvia conduit 1 and is admixed with a hereinafter described hydrogen-richgaseous stream which is carried via conduit 12 and the resultingadmixture is introduced via conduit 2 into dehydrogenation zone 3 todehydrogenate at least a portion of the propane stream to providedehydrogenated hydrocarbons. A hydrocarbon stream comprisingdehydrogenated hydrocarbons and unconverted dehydrogenatablehydrocarbons is removed from dehydrogenation zone 3 via conduit 4 andadmixed with a hereinafter described recycle stream containing hydrogenand minor quantities of hydrocarbon provided via conduit 16 and theresulting admixture is introduced via conduit 5 into compressor 6. Theresulting compressed stream is transported from compressor 6 via conduit7, cooled and introduced into vapor-liquid separator 8. A resultingliquid hydrocarbon product stream containing dehydrogenated hydrocarbonsand dehydrogenatable hydrocarbons is removed from vapor-liquid separator8 via conduit 10 and recovered via conduit 10 and conduit 18. A gaseousstream comprising hydrogen and hydrocarbons is removed from vapor-liquidseparator 8 via conduit 9 and is introduced via conduit 9 intoadsorption zone 11. A hydrogen-rich gaseous stream is removed fromadsorption zone 11 via conduit 12 and at least a portion is recycled viaconduit 12 as previously described. A net hydrogen-rich gaseous streamis removed from the process and recovered via conduit 13. A streamcontaining desorbed hydrocarbon is removed from adsorption zone 11 viaconduit 14 and introduced into chiller 15. A resulting liquidhydrocarbon product stream containing dehydrogenated hydrocarbons anddehydrogenatable hydrocarbons is removed from chiller 15 via conduit 17and recovered via conduit 18. A gaseous stream containing hydrogen andhydrocarbons is removed from chiller 15 via conduit 16 and recycled tocompressor 6 as previously described.

The following illustrative embodiment is presented for the purpose offurther demonstrating the process of the present invention and toindicate the benefits afforded without undue limitation by theutilization thereof in maximizing the recovery of dehydrogenatedhydrocarbons in an economical manner. The following data were notobtained by the actual performance of the present invention, but areconsidered prospective and reasonably illustrative of the expectedperformance of the invention as determined by engineering calculations.

ILLUSTRATIVE EMBODIMENT

A feed stream having a flow rate in an amount 10×10⁶ standard cubic feetper day (10 MM SCFD), and having a composition of 50 volume percenthydrogen and 50 volume percent 1-butene is selected to demonstrate theprocess of the present invention. Although a simplified composition forthe feed stream is used as the model, it is understood that the feedstream may contain other components having both higher and lower boilingpoints as compared to 1-butene. Since dehydrogenation zones are notoperated at 100% conversion per pass, butane is recycled for subsequentconversion and is also present in the streams described.

The feed stream, as described hereinabove, is representative of aneffluent from a catalytic dehydrogenation zone which is operated atclose to atmospheric pressure. This stream is compressed to a pressureof 140 psig (965 kPa gauge) and cooled to a temperature of about 100° F.(38° C.) which causes the condensation of a portion of the 1-butene.

The resulting condensed and cooled stream is introduced into avapor-liquid separator which produces an overhead vapor stream in anamount of 8.4 MM SCFD containing 59.4 volume percent hydrogen and 40.6volume percent butene, and a bottom liquid stream in an amount equal toabout 1.6 MM SCFD. The effluent gas stream from the vapor-liquidseparator together with a hereinafter-described recycle stream isintroduced into an adsorber bed containing an adsorbent whichselectively adsorbs 1-butene at conditions which include a pressure ofabout 120 psig (827 kPa gauge) and a temperature of about 100° F. (38°C.). A high purity hydrogen-rich gaseous stream is then recovered fromthe adsorber bed and containing 99.999 volume percent hydrogen whilecontaining only 10 ppm 1-butene. A portion of the hydrogen contained inthe feed is used to regenerate a spent adsorber bed to remove adsorbed1-butene thereby producing a hydrocarbon vapor stream in an amount of5.0 MM SCFD containing 36.2 volume percent hydrogen and 63.8 volumepercent 1-butene. This hydrocarbon vapor stream is cooled in a chillerto 0° F. (-18° C.). A liquid 1-butene stream is produced from theeffluent from the chiller in an amount equal to about 1.7 MM SCFD andcontaining 99.9 volume percent 1-butene and 0.1 volume percent hydrogen.A gas stream from the chiller is produced in an amount of 3.3 MM SCFDcontaining 55.4 volume percent hydrogen and 44.6 volume percent 1-buteneand is recycled to the feed stream.

The foregoing description, drawing and illustrative embodiment clearlyillustrate the advantages encompassed by the method of the presentinvention and the benefits to be afforded with the use thereof.

What is claimed:
 1. A process for the dehydrogenation of adehydrogenatable hydrocarbon which process comprises:(a) contacting saiddehydrogenatable hydrocarbon with a dehydrogenation catalyst in adehydrogenation zone at dehydrogenation conditions to produce ahydrocarbon effluent stream comprising dehydrogenated hydrocarbons,unconverted dehydrogenatable hydrocarbons and hydrogen; (b) compressingsaid hydrogen effluent stream comprising dehydrogenated hydrocarbons,unconverted dehydrogenatable hydrocarbons and hydrogen to produce acompressed stream; (c) cooling said compressed stream to a temperatureless than about 150° F. (65° C.); (d) introducing the resultingcompressed, cooled stream produced in step (c) into a vapor-liquidseparator; (e) withdrawing from said vapor-liquid separator a liquidstream comprising at least a portion of said dehydrogenated hydrocarbonsand said unconverted dehydrogenatable hydrocarbon contained in saidhydrocarbon effluent stream; (f) withdrawing from said vapor-liquidseparator a hydrogen-rich gaseous stream comprising at least a portionof said dehydrogenated hydrocarbons and unconverted dehydrogenatablehydrocarbons; (g) passing said hydrogen-rich gaseous stream from step(f) to a first adsorber bed containing adsorbent having a adsorptivecapacity for hydrocarbons at effective adsorption conditions; (h)withdrawing a hydrogen-rich gaseous stream having a reducedconcentration of hydrocarbons from said first absorber bed; (i)withdrawing a stream rich in hydrocarbons from a second adsorber bedcontaining adsorbent having adsorptive capacity for hydrocarbons whichbed has become loaded with hydrocarbons and is undergoing desorption;(j) cooling said stream rich in hydrocarbons from step (i) to atemperatures less than about 100° F. (38° C.); (k) introducing theresulting cooled stream produced in step (j) into a vapor-liquidseparator to produce a vapor stream comprising hydrogen and a liquidstream comprising dehydrogenated hydrocarbon; (l) recycling said vaporstream comprising hydrogen recovered in step (k) to step (b); and (m)recovering a hydrocarbon stream comprising a hydrogenated hydrocarbon.2. The process of claim 1 wherein at least a portion of saidhydrogen-rich gaseous stream from step (f) is recycled to saiddehydrogenation zone.
 3. The process of claim 1 wherein said liquidstream comprising at least a portion of said dehydrogenated hydrocarbonsand said unconverted dehydrogenatable hydrocarbons produced in step (e)is separated to produce a dehydrogenated hydrocarbon product stream andan unconverted dehydrogenatable hydrocarbon stream.
 4. The process ofclaim 3 wherein said unconverted dehydrogenatable hydrocarbon stream isrecycled to said dehydrogenation zone.
 5. The process of claim 1 whereinsaid hydrogenatable hydrocarbon feedstock is selected from the groupconsisting of ethane, propane, butane and pentane.
 6. The process ofclaim 1 wherein said dehydrogenation conditions include a temperaturefrom about 752° F. (400° C.) to about 1652° F. (900° C.), a pressurefrom about 0.01 to about 10 atmospheres absolute, a liquid hourly spacevelocity from about 0.1 to about 100 hr⁻¹ and a hydrogen to hydrocarbonmole ratio from about 0.01:1 to about 40:1.
 7. The process of claim 1wherein said dehydrogenatable catalyst comprises a platinum group metalcomponent, an alkali metal component and a porous inorganic carriermaterial.
 8. The process of claim 1 wherein second adsorber bedcontaining adsorbent is desorbed by passing at least a portion of saidhydrogen-rich gaseous stream produced in step (f) to desorb hydrocarbonsthereby regenerating said adsorbent.
 9. The process of claim 1 whereinsaid compressed stream in step (b) is compressed to a pressure in therange from about 1 psig (6.895 kPa gauge) to about 1000 psig (6895 kPagauge).
 10. The process of claim 1 wherein said cooling of saidcompressed stream in step (c) is in the temperature range from about 60°F. (16° C.) to about 150° F. (65° C.).
 11. The process of claim 1wherein said first adsorber bed is operated at conditions which includea pressure from about 1 psig (6.895 kPa gauge) to about 1000 psig (6895kPa gauge) and a temperature from about -20° F. (-29° C.) to about 150°F. (65.5° C.).
 12. The process of claim 1 wherein said cooling of saidstream rich in hydrocarbons in step (j) is in the temperature range fromabout -20° F. (-29° C.) to about 100° F. (38° C.).
 13. A process for thedehydrogenation of a dehydrogenatable hydrocarbon which processcomprises:(a) contacting said dehydrogenatable hydrocarbon with adehydrogenation catalyst in a dehydrogenation zone at dehydrogenationconditions which include a temperature from about 752° F. (400° C.) toabout 1652° F. (900° C.), a pressure from about 0.01 to about 10atmospheres absolute, a liquid hourly space velocity from about 0.1 toabout 100 hr⁻¹ and a hydrogen to hydrocarbon mole ratio from about0.01:1 to about 40:1 to produce a hydrocarbon effluent stream comprisingdehydrogenated hydrocarbons, unconverted dehydrogenatable hydrocarbonsand hydrogen; (b) compressing said hydrocarbon effluent streamcomprising dehydrogenated hydrocarbons, unconverted dehydrogenatablehydrocarbons and hydrogen to a pressure in the range from about 1 psig(6.895 kPa gauge) to about 1000 psig (6895 kPa gauge) to produce acompressed stream; (c) cooling said compressed stream to a temperaturein the range from about 60° F. (16° C.) to about 120° F. (49° C.); (d)introducing the resulting compressed, cooled stream produced in step (c)into a vapor-liquid separator; (e) withdrawing from said vapor-liquidseparator a liquid stream comprising at least a portion of saiddehydrogenated hydrocarbons and said unconverted dehydrogenatablehydrocarbon contained in said hydrocarbon effluent stream; (f)withdrawing from said vapor-liquid separator a hydrogen-rich gaseousstream comprising at least a portion of said dehydrogenated hydrocarbonsand unconverted dehydrogenatable hydrocarbons; (g) passing saidhydrogen-rich gaseous stream from step (f) to a first adsorber bedcontaining adsorbent having adsorptive capacity for hydrocarbons ateffective adsorption conditions; (h) withdrawing a hydrogen-rich gaseousstream having a reduced concentration of hydrocarbons from said firstadsorber bed; (i) withdrawing a stream rich in hydrocarbons from asecond adsorber bed containing adsorbent having adsorptive capacity forhydrocarbons which bed has become loaded with hydrocarbons and isundergoing desorption; (j) cooling said stream rich in hydrocarbons fromstep (i) to a temperature in the range from about -20° F. (-29° C.) toabout 100° F. (38° C.); (k) introducing the resulting cooled streamproduced in step (j) into a vapor-liquid separator to produce a vaporstream comprising hydrogen and a liquid stream comprising dehydrogenatedhydrocarbon; (l) recycling said vapor stream comprising hydrogenrecovered in step (k) to step (b); and (m) recovering a hydrocarbonstream comprising a dehydrogenated hydrocarbon.